The flameproofing requirements with regard to construction materials, components and materials are extensive. Thus, for example, construction materials can be classified according to DIN 4102, components for electrical equipment according to UL 94 or IEC-60695-2, components for railway vehicles according to DIN 5510 and furniture according to BS 5852 and can be provided with an appropriate flame-retardant treatment for their application. For example, the treatment of aircraft (e.g. FAR 25.853) or ships (e.g. IMO A.652 (16)) has to meet particular requirements. An overview of numerous tests and requirements is given, for example, by Jürgen Troitzsch, “Plastics Flammability Handbook”, 2004, Carl Hanser Verlag, Munich.
In addition, the fireproofing requirements are constantly increasing. Thus, for example, new European standards which are intended to replace the existing national test standards set substantially higher flameproofing requirements. Thus, the SBI test (EN 13823), for example, requires not only the fire behavior but also the smoke density be taken into account. The new standard proposed for a railway vehicle (prEN 45545) takes into account, for example, fume density and fume toxicity. Requirements regarding the fume toxicity, which is often determined by measurement of, inter alia, hydrogen halide concentrations in the fume, can, for example, make the use of tried and tested halogen-containing flameproofing agents impossible. This means that, for many fields of use, a tried and tested and functionally flameproof treatment has to be revised with regard to new requirements in line with standards.
In addition to purely fire aspects, such as, for example, ignitability or flammability, which a component, construction material, material or additive has to meet, there are also further properties which have to be taken into account. Thus, the term fogging which is customary in the automotive industry (e.g. DIN EN 14288) describes emissions which are released by materials and can be deposited in the passenger compartment. The use of such volatile additives is likewise to be avoided.
Further requirements which not only result from test standards but are also required by customers or end users are: halogen-free, nonvolatile, cannot be washed out, economical, usable without changing the process in production, no influence on the properties of the end product.
If leather is used in vehicles, for example as seat covering, or in the equipment of buildings, for example as seating, it must meet the respective fireproof requirements. At the same time, the appearance, hand, and odor, i.e. the organoleptic perception of the natural material leather, should not be excessively influenced on treatment with flameproofing agents. In addition, the flame-retardant finishing, i.e. the incorporation of a flameproofing agent into the leather, should set no particular requirements with regard to the customary production and processing of the leather. The additives required for flameproofing the leather should be safe and should not necessitate any special requirements with regard to handling or processing.
Flame-retardant leathers are already known. However, the finishes described have the disadvantage that they are either halogen-containing or can be washed out. Flame-retardant leather finishes based on halogen-containing alkyl or aryl phosphates are disclosed in GB 2 084 622 A. The use of inorganic salts, such as sodium bromide and boric acid derivatives, is described in K. Donmez, W. E. Kallenberger, J. Am. Leather Chem. Assoc., 1992, 87, 1-19. In order to provide leather with flame-retardant treatment, a separate operation is required. Such flame-retardant finishes adversely affect the properties of the leather and, owing to the halogen content, cause high fume densities and fume toxicities.
GB 434,423 describes a leather finish based on cellulose derivatives which contains tricresyl phosphate and other substances as softeners for the finish, in order to avoid embrittlement and flaking of the decorative protective layer. The flame retardance of the leather is, however, not a subject of this patent.
U.S. Pat. No. 2,635,060 describes fatliquoring emulsions which contain, for example, tricresyl phosphate in small amounts as a softener in combination with other softening substances, such as, for example, dibutyl phthalate. In addition to numerous advantages which are ascribed to such an emulsion, the flame retardance of the leather which was treated with such a phosphate-containing emulsion is on the other hand absent. Only better softening effect of a softening combination is mentioned as an advantage of such softener combinations. Experience shows that, if they are used as flameproofing agents, for example in plastics or textiles, organic phosphates must be used in substantially higher doses than described in the patent. Formulations for imitation leather based on flexible PVC, as described in Becker/Braun, Kunststoff Handbuch Polyvinylchlorid [Plastics Handbook Polvinyl chloride], Vol. 2/1, Carl Hanser Verlag, Munich, Vienna, 1986, may be mentioned as an example here. Substantial flame retardance is present in the case of PVC imitation leather provided with a flame retardant treatment using phosphoric acid esters only at a content of 20% of phosphoric acid esters. In practice, the content is even higher.
A process for the flame-retardant treatment of leather, in which organic phosphate esters and tetrakis(hydroxyalkyl)phosphonium halides are used, is described in U.S. Pat. No. 3,419,344. This process has several disadvantages. The flame retardance, which is distinguished in particular by self-extinguishing and absence of continued glowing of the ignited leather, is accordingly achieved only if the leather is subjected to a complicated, two-stage aftertreatment. In the first stage, the leather is treated with a tetrakis(hydroxyalkyl)phosphonium halide for retanning and in the second stage with an organic phosphoric acid ester. It is expressly pointed out that two operations are required for this purpose. Moreover, the aim of achieving a halogen-free finish cannot be achieved with the use of tetrakis(hydroxyalkyl)phosphonium halides.
Flame-retardant leather which contains halogenated organic phosphates is described in GB 2 084 622 A. In every case, halogen-containing compounds are required for the flame-retardant treatment of the leather.
The object was to find auxiliaries and processes for the production of a flame-retardant leather which is self-extinguishing and reacts without continued glowing to the action of an ignition flame for a limited time. The flame-retardant treatment should be economical and based on comparatively cheap as well as accessible products. The flame-retardant finish or the auxiliaries used for this purpose should be halogen-free. The properties of the leather should not be adversely affected. The incorporation should be possible without special operations, as described in U.S. Pat. No. 3,419,344, in the course of the customary further processing of the raw hide.